Evaluation of growth, survival, and recruitment of chinook salmon in Southeast Alaska rivers

Abstract

Recent reductions in the run sizes of Chinook Salmon Oncorhynchus tshawytscha in Southeast Alaska have resulted in social and economic hardships within the region. Pacific salmon yearclass strength may be determined by size-selective processes during the early marine phase of their life cycle; however, the relative importance of growth during freshwater and marine residence in determining recruitment success is unknown. A scale-based retrospective analysis was conducted to examine the effects of freshwater and annual marine growth and early marine conditions on survival to reproductive maturity for female Chinook Salmon by brood year (BY) in the Taku (BYs 1979 -- 1985, 1990 -- 1999, 2002 -- 2004) and Unuk (BYs 1981 -- 1983, 1986 -- 1988, 1994 -- 2003, 2005 -- 2006) rivers. First-year marine growth was positively related to survival and total return for Chinook Salmon stocks from both systems. Growth during freshwater residence (i.e., size-at-ocean entry) was not related to survival or total return of either stock. In addition, there was a positive relationship between marine survival of Unuk River Chinook Salmon and sea-surface temperatures in Upper Chatham Strait, Icy Strait, and Auke Bay Monitor (P = 0.04) during early marine residence. The results of my research highlight the importance of growth and marine conditions during the first year at sea in determining the survival of Chinook Salmon in Southeast Alaska and suggest that current declines in run sizes and survival of stocks within this region may be the attributed to poor growth conditions or growth during early marine residence.